Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.95   6.664%   $265.54   $265.54   $265.55   $265.50  
  Purchase #2 $114.47   9.274%   $125.0859   $125.09   $125.10   $125.10  
  Purchase #3 $242.77   11.600%   $270.9313   $270.93   $270.95   $270.90  
  Purchase #4 $70.72   13.730%   $80.4299   $80.43   $80.45   $80.40  
  Purchase #5 $158.83   10.612%   $175.685   $175.69   $175.70   $175.70  
  Purchase #6 $201.93   5.631%   $213.3007   $213.30   $213.30   $213.30  
  Purchase #7 $216.86   13.826%   $246.8431   $246.84   $246.85   $246.80  
  7 purchase totals = $1,254.53       $1,377.8159   $1,377.82   $1,377.90   $1,377.70